Pressurizing Fuel Tank

[TCD]

Howdy,

I am trouble shooting a case of fuel feeding failure. I have installed a Schrader valve in to a standard fuel cap. I want to also install a pressure gauge in the fuel cap to make sure that I am safely pressurizing the system.

What is the maximum pressure I should use to test the fuel circuit and bleed the fuel system when pressurizing the system from the fuel tank?

Thanks,
Tom

 

[Csm Davis]

3 psi you can hold your finger over a hole with enough pressure to rupture the tanks.

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[rosco]

A few times I've wanted to prime or flush a fuel system - quick. I've taken a shop rag in my hand an a blow gun in the other. Stick the blow gun in the neck of the tank, cover it over with the rag & hand, while discharging the blow gun into the tank. Be careful, depending on the pressure of your compressor, you can still over charge the tank. At any rate, the procedure will quickly flush a line, charge a filter, or find a leak.

 

[86m1028]

Wondering how you can over pressurize an m939 series fuel tank which is vented ?

 

[TCD]

Thanks everyone! Ill use a small handheld bicycle pump for the task.

86m1028, I have read that the tank vents are routinely blocked for this to work, typically where the vent manifold line goes into the intake pipe. I'm planning on capping the two vents at the tank as I want to shorten and cleanup the two vent lines anyway.

Thanks again,
Tom

 

[86m1028]

Thanks everyone! Ill use a small handheld bicycle pump for the task.

86m1028, I have read that the tank vents are routinely blocked for this to work, typically where the vent manifold line goes into the intake pipe. I'm planning on capping the two vents at the tank as I want to shorten and cleanup the two vent lines anyway.

Thanks again,
Tom

Tom, Keep us posted.
Im working on dual tanks on an m936 right now.
Rebuilding tank selector & replacing ALL flexible fuel lines.

 

[Suprman]

You cant really over pressure the tank it vents. On the A2 trucks the lines that come off the big separator in the drivers footwell area commonly rub thru.

 

[TCD]

For further info about my project please see:

http://www.steelsoldiers.com/showthread.php?161814-923-a2-No-water-separator

Suprman, Do you know exactly what the function of the valve in picture #1 of the above post does? I hope to completely trace it out this weekend as there are several connections. I am currently planning on removing the mystery valve completely and simply add a water separator/filter inline with the fuel feed.

All info greatly appreciated.

Thanks,
Tom

PS: All future posts relating to this project will be posted in the above linked thread.
t

 

[Suprman]

Those look like air lines not fuel. Trace backwards from the lift pump. Did you replace the spin on filter on the block? With no large filter that smaller one might get pretty clogged up.

 

[Ford Mechanic]

I installed a Schrader valve in mine also for bleeding. I just bump it with the air chuck, mine works with out blocking the vents.

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[ross165123]

I ran a line from the air tank to the vent on the firewall with a regulator and pluged the vent cap. Then set it to 5psi to prim my bad injector pump. I once set it to 20psi by mistake and nothing blew up just popped out a dent.

 

[stanleycr1]

If I disconnect the fuel line from the lift pump and blow on it there is gurgling in the fuel tank. Is there not a check valve?

 

[red]

No check valve